E3 ubiquitin-protein ligase that acts as a regulator of motor axon elongation. Required for efficient motor axon extension in the dorsal forelimb by enhancing the transcriptional responses of the SMAD1/SMAD5/SMAD8 effectors, which are activated downstream of BMP. Acts by mediating ubiquitination and degradation of SMAD inhibitors such as SMAD6, SMAD7, SKI and SNON isoform of SKIL.
